Linux Programmer's Manual CONSOLE_CODES

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CONSOLE_CODES(4)                                     Linux Programmer's Manual                                    CONSOLE_CODES(4)



NAME
       console_codes - Linux console escape and control sequences

DESCRIPTION
       The  Linux  console  implements a large subset of the VT102 and ECMA-48/ISO 6429/ANSI X3.64 terminal controls, plus certain
       private-mode sequences for changing the color palette, character-set mapping, etc.  In the tabular descriptions below,  the
       second column gives ECMA-48 or DEC mnemonics (the latter if prefixed with DEC) for the given function.  Sequences without a
       mnemonic are neither ECMA-48 nor VT102.

       After all the normal output processing has been done, and a stream of characters arrives at the console driver  for  actual
       printing, the first thing that happens is a translation from the code used for processing to the code used for printing.

       If  the  console  is  in UTF-8 mode, then the incoming bytes are first assembled into 16-bit Unicode codes.  Otherwise each
       byte is transformed according to the current mapping table (which translates it to a Unicode  value).   See  the  Character
       Sets section below for discussion.

       In  the normal case, the Unicode value is converted to a font index, and this is stored in video memory, so that the corre‐
       sponding glyph (as found in video ROM) appears on the screen.  Note that the use of Unicode (and the design of the PC hard‐
       ware) allows us to use 512 different glyphs simultaneously.

       If  the  current  Unicode  value  is a control character, or we are currently processing an escape sequence, the value will
       treated specially.  Instead of being turned into a font index and rendered as a glyph, it may trigger  cursor  movement  or
       other control functions.  See the Linux Console Controls section below for discussion.

       It  is  generally not good practice to hard-wire terminal controls into programs.  Linux supports a terminfo(5) database of
       terminal capabilities.  Rather than emitting console escape sequences by hand, you will almost always want to  use  a  ter‐
       minfo-aware screen library or utility such as ncurses(3), tput(1), or reset(1).

   Linux Console Controls
       This  section describes all the control characters and escape sequences that invoke special functions (i.e., anything other
       than writing a glyph at the current cursor location) on the Linux console.

       Control characters

       A character is a control character if (before transformation according to the mapping table) it has one of the 14 codes  00
       (NUL),  07  (BEL), 08 (BS), 09 (HT), 0a (LF), 0b (VT), 0c (FF), 0d (CR), 0e (SO), 0f (SI), 18 (CAN), 1a (SUB), 1b (ESC), 7f
       (DEL).  One can set a "display control characters" mode (see below), and allow 07, 09, 0b, 18, 1a, 7f to  be  displayed  as
       glyphs.   On  the  other hand, in UTF-8 mode all codes 00-1f are regarded as control characters, regardless of any "display
       control characters" mode.

       If we have a control character, it is acted upon immediately and then discarded (even in the middle of an escape  sequence)
       and the escape sequence continues with the next character.  (However, ESC starts a new escape sequence, possibly aborting a
       previous unfinished one, and CAN and SUB abort any escape sequence.)  The recognized control characters are  BEL,  BS,  HT,
       LF, VT, FF, CR, SO, SI, CAN, SUB, ESC, DEL, CSI.  They do what one would expect:

       BEL (0x07, ^G) beeps;

       BS (0x08, ^H) backspaces one column (but not past the beginning of the line);

       HT (0x09, ^I) goes to the next tab stop or to the end of the line if there is no earlier tab stop;

       LF  (0x0A,  ^J),  VT  (0x0B, ^K) and FF (0x0C, ^L) all give a linefeed, and if LF/NL (new-line mode) is set also a carriage
              return;

       CR (0x0D, ^M) gives a carriage return;

       SO (0x0E, ^N) activates the G1 character set;

       SI (0x0F, ^O) activates the G0 character set;

       CAN (0x18, ^X) and SUB (0x1A, ^Z) interrupt escape sequences;

       ESC (0x1B, ^[) starts an escape sequence;

       DEL (0x7F) is ignored;

       CSI (0x9B) is equivalent to ESC [.

       ESC- but not CSI-sequences

       ESC c     RIS      Reset.
       ESC D     IND      Linefeed.
       ESC E     NEL      Newline.
       ESC H     HTS      Set tab stop at current column.
       ESC M     RI       Reverse linefeed.
       ESC Z     DECID    DEC private identification. The kernel returns the
                          string  ESC [ ? 6 c, claiming that it is a VT102.
       ESC 7     DECSC    Save    current    state    (cursor   coordinates,
                          attributes, character sets pointed at by G0, G1).
       ESC 8     DECRC    Restore state most recently saved by ESC 7.
       ESC [     CSI      Control sequence introducer
       ESC %              Start sequence selecting character set
       ESC % @               Select default (ISO 646 / ISO 8859-1)
       ESC % G               Select UTF-8
       ESC % 8               Select UTF-8 (obsolete)
       ESC # 8   DECALN   DEC screen alignment test - fill screen with E's.
       ESC (              Start sequence defining G0 character set
       ESC ( B               Select default (ISO 8859-1 mapping)
       ESC ( 0               Select VT100 graphics mapping
       ESC ( U               Select null mapping - straight to character ROM
       ESC ( K               Select user mapping - the map that is loaded by
                             the utility mapscrn(8).
       ESC )              Start sequence defining G1
                          (followed by one of B, 0, U, K, as above).
       ESC >     DECPNM   Set numeric keypad mode
       ESC =     DECPAM   Set application keypad mode
       ESC ]     OSC      (Should be: Operating  system  command)  ESC  ]  P
                          nrrggbb:  set  palette,  with parameter given in 7
                          hexadecimal digits after the final P :-(.  Here  n
                          is  the  color  (0-15),  and  rrggbb indicates the
                          red/green/blue values (0-255).   ESC  ]  R:  reset
                          palette

       ECMA-48 CSI sequences

       CSI  (or  ESC  [)  is  followed by a sequence of parameters, at most NPAR (16), that are decimal numbers separated by semi‐
       colons.  An empty or absent parameter is taken to be 0.  The sequence of parameters may be preceded by  a  single  question
       mark.

       However,  after  CSI [ (or ESC [ [) a single character is read and this entire sequence is ignored.  (The idea is to ignore
       an echoed function key.)

       The action of a CSI sequence is determined by its final character.

       @   ICH       Insert the indicated # of blank characters.
       A   CUU       Move cursor up the indicated # of rows.
       B   CUD       Move cursor down the indicated # of rows.
       C   CUF       Move cursor right the indicated # of columns.
       D   CUB       Move cursor left the indicated # of columns.
       E   CNL       Move cursor down the indicated # of rows, to column 1.
       F   CPL       Move cursor up the indicated # of rows, to column 1.
       G   CHA       Move cursor to indicated column in current row.
       H   CUP       Move cursor to the indicated row, column (origin at 1,1).
       J   ED        Erase display (default: from cursor to end of display).
                     ESC [ 1 J: erase from start to cursor.
                     ESC [ 2 J: erase whole display.
                     ESC [ 3 J: erase whole display including scroll-back

                                buffer (since Linux 3.0).
       K   EL        Erase line (default: from cursor to end of line).
                     ESC [ 1 K: erase from start of line to cursor.
                     ESC [ 2 K: erase whole line.
       L   IL        Insert the indicated # of blank lines.
       M   DL        Delete the indicated # of lines.
       P   DCH       Delete the indicated # of characters on the current line.
       X   ECH       Erase the indicated # of characters on the current line.
       a   HPR       Move cursor right the indicated # of columns.
       c   DA        Answer ESC [ ? 6 c: "I am a VT102".
       d   VPA       Move cursor to the indicated row, current column.
       e   VPR       Move cursor down the indicated # of rows.
       f   HVP       Move cursor to the indicated row, column.
       g   TBC       Without parameter: clear tab stop at the current position.
                     ESC [ 3 g: delete all tab stops.
       h   SM        Set Mode (see below).
       l   RM        Reset Mode (see below).
       m   SGR       Set attributes (see below).
       n   DSR       Status report (see below).
       q   DECLL     Set keyboard LEDs.
                     ESC [ 0 q: clear all LEDs
                     ESC [ 1 q: set Scroll Lock LED
                     ESC [ 2 q: set Num Lock LED
                     ESC [ 3 q: set Caps Lock LED
       r   DECSTBM   Set scrolling region; parameters are top and bottom row.
       s   ?         Save cursor location.
       u   ?         Restore cursor location.
       `   HPA       Move cursor to indicated column in current row.

       ECMA-48 Set Graphics Rendition

       The ECMA-48 SGR sequence ESC [ parameters m sets display attributes.  Several attributes can be set in the  same  sequence,
       separated  by  semicolons.   An  empty parameter (between semicolons or string initiator or terminator) is interpreted as a
       zero.

       param   result
       0       reset all attributes to their defaults
       1       set bold
       2       set half-bright (simulated with color on a color display)
       4       set underscore (simulated with color on a color  display)
               (the  colors  used  to  simulate dim or underline are set
               using ESC ] ...)
       5       set blink
       7       set reverse video
       10      reset selected mapping, display control flag, and  toggle
               meta flag (ECMA-48 says "primary font").
       11      select null mapping, set display control flag, reset tog‐
               gle meta flag (ECMA-48 says "first alternate font").
       12      select null mapping, set display control flag, set toggle
               meta  flag  (ECMA-48  says "second alternate font").  The
               toggle meta flag causes the high bit of a byte to be tog‐
               gled before the mapping table translation is done.
       21      set normal intensity (ECMA-48 says "doubly underlined")
       22      set normal intensity
       24      underline off
       25      blink off
       27      reverse video off
       30      set black foreground
       31      set red foreground
       32      set green foreground
       33      set brown foreground
       34      set blue foreground
       35      set magenta foreground
       36      set cyan foreground
       37      set white foreground

       38      set underscore on, set default foreground color
       39      set underscore off, set default foreground color
       40      set black background
       41      set red background
       42      set green background
       43      set brown background
       44      set blue background
       45      set magenta background
       46      set cyan background
       47      set white background
       49      set default background color

       ECMA-48 Mode Switches

       ESC [ 3 h
              DECCRM (default off): Display control chars.

       ESC [ 4 h
              DECIM (default off): Set insert mode.

       ESC [ 20 h
              LF/NL (default off): Automatically follow echo of LF, VT or FF with CR.

       ECMA-48 Status Report Commands

       ESC [ 5 n
              Device status report (DSR): Answer is ESC [ 0 n (Terminal OK).

       ESC [ 6 n
              Cursor position report (CPR): Answer is ESC [ y ; x R, where x,y is the cursor location.

       DEC Private Mode (DECSET/DECRST) sequences

       These are not described in ECMA-48.  We list the Set Mode sequences; the Reset Mode sequences are obtained by replacing the
       final 'h' by 'l'.

       ESC [ ? 1 h
              DECCKM (default off): When set, the cursor keys send an ESC O prefix, rather than ESC [.

       ESC [ ? 3 h
              DECCOLM (default off = 80 columns): 80/132 col mode switch.  The driver sources note that this alone does  not  suf‐
              fice; some user-mode utility such as resizecons(8) has to change the hardware registers on the console video card.

       ESC [ ? 5 h
              DECSCNM (default off): Set reverse-video mode.

       ESC [ ? 6 h
              DECOM (default off): When set, cursor addressing is relative to the upper left corner of the scrolling region.

       ESC [ ? 7 h
              DECAWM  (default  on): Set autowrap on.  In this mode, a graphic character emitted after column 80 (or column 132 of
              DECCOLM is on) forces a wrap to the beginning of the following line first.

       ESC [ ? 8 h
              DECARM (default on): Set keyboard autorepeat on.

       ESC [ ? 9 h
              X10 Mouse Reporting (default off): Set reporting mode to 1 (or reset to 0)—see below.

       ESC [ ? 25 h
              DECTECM (default on): Make cursor visible.

       ESC [ ? 1000 h
              X11 Mouse Reporting (default off): Set reporting mode to 2 (or reset to 0)—see below.

       Linux Console Private CSI Sequences

       The following sequences are neither ECMA-48 nor native VT102.  They are native to the Linux console driver.  Colors are  in
       SGR parameters: 0 = black, 1 = red, 2 = green, 3 = brown, 4 = blue, 5 = magenta, 6 = cyan, 7 = white.

       ESC [ 1 ; n ]       Set color n as the underline color
       ESC [ 2 ; n ]       Set color n as the dim color
       ESC [ 8 ]           Make the current color pair the default attributes.
       ESC [ 9 ; n ]       Set screen blank timeout to n minutes.
       ESC [ 10 ; n ]      Set bell frequency in Hz.
       ESC [ 11 ; n ]      Set bell duration in msec.
       ESC [ 12 ; n ]      Bring specified console to the front.
       ESC [ 13 ]          Unblank the screen.
       ESC [ 14 ; n ]      Set the VESA powerdown interval in minutes.

   Character Sets
       The kernel knows about 4 translations of bytes into console-screen symbols.  The four tables are: a) Latin1 -> PC, b) VT100
       graphics -> PC, c) PC -> PC, d) user-defined.

       There are two character sets, called G0 and G1, and one of them is the current character set.  (Initially G0.)   Typing  ^N
       causes G1 to become current, ^O causes G0 to become current.

       These  variables G0 and G1 point at a translation table, and can be changed by the user.  Initially they point at tables a)
       and b), respectively.  The sequences ESC ( B and ESC ( 0 and ESC ( U and ESC ( K cause G0 to point at translation table a),
       b),  c)  and  d), respectively.  The sequences ESC ) B and ESC ) 0 and ESC ) U and ESC ) K cause G1 to point at translation
       table a), b), c) and d), respectively.

       The sequence ESC c causes a terminal reset, which is what you want if the screen is all  garbled.   The  oft-advised  "echo
       ^V^O"  will  only  make G0 current, but there is no guarantee that G0 points at table a).  In some distributions there is a
       program reset(1) that just does "echo ^[c".  If your terminfo entry for the console is correct (and has an entry  rs1=\Ec),
       then "tput reset" will also work.

       The  user-defined  mapping  table can be set using mapscrn(8).  The result of the mapping is that if a symbol c is printed,
       the symbol s = map[c] is sent to the video memory.  The bitmap that corresponds to s is found in the character ROM, and can
       be changed using setfont(8).

   Mouse Tracking
       The mouse tracking facility is intended to return xterm(1)-compatible mouse status reports.  Because the console driver has
       no way to know the device or type of the mouse, these reports are returned in the console input stream only when  the  vir‐
       tual  terminal driver receives a mouse update ioctl.  These ioctls must be generated by a mouse-aware user-mode application
       such as the gpm(8) daemon.

       The mouse tracking escape sequences generated by xterm(1) encode numeric parameters in a  single  character  as  value+040.
       For example, '!' is 1.  The screen coordinate system is 1-based.

       The X10 compatibility mode sends an escape sequence on button press encoding the location and the mouse button pressed.  It
       is enabled by sending ESC [ ? 9 h and disabled with ESC [ ? 9 l.  On button press, xterm(1) sends ESC [ M  bxy  (6  charac‐
       ters).   Here b is button-1, and x and y are the x and y coordinates of the mouse when the button was pressed.  This is the
       same code the kernel also produces.

       Normal tracking mode (not implemented in Linux 2.0.24) sends an escape sequence on both button press and release.  Modifier
       information  is  also  sent.  It is enabled by sending ESC [ ? 1000 h and disabled with ESC [ ? 1000 l.  On button press or
       release, xterm(1) sends ESC [ M bxy.  The low two bits of b encode button information: 0=MB1 pressed, 1=MB2 pressed,  2=MB3
       pressed,  3=release.   The  upper  bits encode what modifiers were down when the button was pressed and are added together:
       4=Shift, 8=Meta, 16=Control.  Again x and y are the x and y coordinates of the mouse  event.   The  upper  left  corner  is
       (1,1).

   Comparisons With Other Terminals
       Many  different terminal types are described, like the Linux console, as being "VT100-compatible".  Here we discuss differ‐
       ences between the Linux console and the two most important others, the DEC VT102 and xterm(1).

       Control-character handling

       The VT102 also recognized the following control characters:

       NUL (0x00) was ignored;

       ENQ (0x05) triggered an answerback message;

       DC1 (0x11, ^Q, XON) resumed transmission;

       DC3 (0x13, ^S, XOFF) caused VT100 to ignore (and stop transmitting) all codes except XOFF and XON.

       VT100-like DC1/DC3 processing may be enabled by the tty driver.

       The xterm(1) program (in VT100 mode) recognizes the control characters BEL, BS, HT, LF, VT, FF, CR, SO, SI, ESC.

       Escape sequences

       VT100 console sequences not implemented on the Linux console:

       ESC N       SS2   Single shift 2. (Select G2 character set for the next
                         character only.)
       ESC O       SS3   Single shift 3. (Select G3 character set for the next
                         character only.)
       ESC P       DCS   Device control string (ended by ESC \)
       ESC X       SOS   Start of string.
       ESC ^       PM    Privacy message (ended by ESC \)
       ESC \       ST    String terminator
       ESC * ...         Designate G2 character set
       ESC + ...         Designate G3 character set

       The program xterm(1) (in VT100 mode) recognizes ESC c, ESC # 8, ESC >, ESC =, ESC D, ESC E, ESC H, ESC M, ESC N, ESC O, ESC
       P  ...  ESC  \,  ESC Z (it answers ESC [ ? 1 ; 2 c, "I am a VT100 with advanced video option") and ESC ^ ... ESC \ with the
       same meanings as indicated above.  It accepts ESC (, ESC ), ESC *,  ESC + followed by 0, A, B for the DEC special character
       and line drawing set, UK, and US-ASCII, respectively.

       The  user  can  configure  xterm(1)  to respond to VT220-specific control sequences, and it will identify itself as a VT52,
       VT100, and up depending on the way it is configured and initialized.

       It accepts ESC ] (OSC) for the setting of certain resources.  In addition to the ECMA-48 string terminator  (ST),  xterm(1)
       accepts a BEL to terminate an OSC string.  These are a few of the OSC control sequences recognized by xterm(1):

       ESC ] 0 ; txt ST        Set icon name and window title to txt.
       ESC ] 1 ; txt ST        Set icon name to txt.
       ESC ] 2 ; txt ST        Set window title to txt.
       ESC ] 4 ; num; txt ST   Set ANSI color num to txt.
       ESC ] 10 ; txt ST       Set dynamic text color to txt.
       ESC ] 4 6 ; name ST     Change log file to name (normally disabled
                               by a compile-time option)
       ESC ] 5 0 ; fn ST       Set font to fn.

       It recognizes the following with slightly modified meaning (saving more state, behaving closer to VT100/VT220):

       ESC 7  DECSC   Save cursor
       ESC 8  DECRC   Restore cursor

       It also recognizes

       ESC F          Cursor to lower left corner of screen (if enabled by
                      xterm(1)'s hpLowerleftBugCompat resource)
       ESC l          Memory lock (per HP terminals).
                      Locks memory above the cursor.
       ESC m          Memory unlock (per HP terminals).
       ESC n   LS2    Invoke the G2 character set.
       ESC o   LS3    Invoke the G3 character set.
       ESC |   LS3R   Invoke the G3 character set as GR.
                      Has no visible effect in xterm.
       ESC }   LS2R   Invoke the G2 character set as GR.
                      Has no visible effect in xterm.
       ESC ~   LS1R   Invoke the G1 character set as GR.
                      Has no visible effect in xterm.

       It also recognizes ESC % and provides a more complete UTF-8 implementation than Linux console.

       CSI Sequences

       Old versions of xterm(1), for example, from X11R5, interpret the blink SGR as a bold SGR.  Later versions which implemented
       ANSI colors, for example, XFree86 3.1.2A in 1995, improved this by allowing the blink attribute to be displayed as a color.
       Modern  versions  of  xterm  implement blink SGR as blinking text and still allow colored text as an alternate rendering of
       SGRs.  Stock X11R6 versions did not recognize the color-setting SGRs until the X11R6.8 release, which incorporated  XFree86
       xterm.   All  ECMA-48  CSI  sequences recognized by Linux are also recognized by xterm, however xterm(1) implements several
       ECMA-48 and DEC control sequences not recognized by Linux.

       The xterm(1) program recognizes all of the DEC Private Mode sequences listed above, but  none  of  the  Linux  private-mode
       sequences.   For  discussion  of  xterm(1)'s  own  private-mode sequences, refer to the Xterm Control Sequences document by
       Edward Moy, Stephen Gildea, and Thomas E. Dickey available with the X distribution.  That document, though terse,  is  much
       longer than this manual page.  For a chronological overview,

           http://invisible-island.net/xterm/xterm.log.html

       details changes to xterm.

       The vttest program

           http://invisible-island.net/vttest/

       demonstrates many of these control sequences.  The xterm(1) source distribution also contains sample scripts which exercise
       other features.

NOTES
       ESC 8 (DECRC) is not able to restore the character set changed with ESC %.

BUGS
       In 2.0.23, CSI is broken, and NUL is not ignored inside escape sequences.

       Some older kernel versions (after 2.0) interpret 8-bit control sequences.  These "C1 controls" use codes  between  128  and
       159  to  replace ESC [, ESC ] and similar two-byte control sequence initiators.  There are fragments of that in modern ker‐
       nels (either overlooked or broken by changes to support UTF-8), but the implementation is incomplete and should be regarded
       as unreliable.

       Linux "private mode" sequences do not follow the rules in ECMA-48 for private mode control sequences.  In particular, those
       ending with ] do not use a standard terminating character.  The OSC (set palette) sequence  is  a  greater  problem,  since
       xterm(1) may interpret this as a control sequence which requires a string terminator (ST).  Unlike the setterm(1) sequences
       which will be ignored (since they are invalid control sequences), the palette sequence will make xterm(1)  appear  to  hang
       (though pressing the return-key will fix that).  To accommodate applications which have been hardcoded to use Linux control
       sequences, set the xterm(1) resource brokenLinuxOSC to true.

       An older version of this document implied that Linux recognizes the ECMA-48 control sequence for  invisible  text.   It  is
       ignored.

SEE ALSO
       console(4), console_ioctl(4), charsets(7)

COLOPHON
       This  page  is  part  of  release 3.35 of the Linux man-pages project.  A description of the project, and information about
       reporting bugs, can be found at http://man7.org/linux/man-pages/.



Linux                                                       2011-09-15                                            CONSOLE_CODES(4)